The present invention relates to intake valve systems for multi-valve engines, and more particularly to methods and apparatus for securing desired air-fuel mixture turbulence level in the combustion chamber in order to achieve optimum combustion.
It is a common goal with vehicle manufacturers today to provide engine and combustion systems which improve fuel economy and, at the same time, reduce undesirable emissions. There are many systems which have been developed which accomplish one or more of these goals and achieve satisfactory results. Some of these systems include, for example, supplying prespecified amounts of fuel and air during certain engine operating conditions, various combustion chamber configurations including shaped bowls in the piston crown in order to secure desired air-fuel mixture and motion under various operating conditions, intake and exhaust valve mechanisms which create desired tumble and/or swirl patterns of in-cylinder flow motion, air-fuel mixture stratifications in the combustion chamber, and the like. Some of these systems are used in particular for direct injection spark ignited (DISI) engines.
Charge motion in the combustion chamber is an important factor for generating turbulence which in turn enhances the burn rate in engines. However, the tumble and/or swirl generation often comes at the expense of discharge coefficient, thus reducing the maximum power output of the engine.
Thus, there is a need for an engine combustion system which creates the desired turbulence in the combustion chamber and yet does not degrade the discharge coefficient.
It is an advantage of the present invention to provide an improved combustion system for an engine.
It is another advantage of the present invention to provide a high turbulence flow field in the combustion chamber without degrading the discharge coefficient or reducing the maximum output power of the engine.
It is a further advantage of the present invention to provide a combustion system which secures high fuel efficiency and at the same time reduces undesirable emissions.
The present invention provides a system and apparatus for achieving these advantages by generating high turbulence levels in the combustion chamber without degrading the discharge coefficient. In accordance with the present invention, a multi-valve engine is provided with at least two independently operated intake valves in each cylinder. One intake port is designed for generation of tumble flow while the other is designed for conventional cylinder filling with high flow efficiency. A high swirl and tumble flow, which decays to in-cylinder turbulence during induction and compression, is provided in the combustion chamber by delaying or advancing the opening of one intake valve relative to the other. Each of the intake valves is operated by an electro-mechanical actuator, or electro-hydraulic actuator, which in turn is activated by the engine controller.
At light load conditions, the necessary mixture motion is generated with the intake valve timing to improve burn rate and thermal efficiency. The tumble valve can be disabled allowing only a swirl flow to be generated in the cylinder. At slightly higher load conditions, a combined tumble and swirl flow can be generated. This is accomplished either by opening the conventional valve for a portion of the process to initial swirl and then opening both valves, or by opening the tumble valve alone to generate a negative direction inclined swirl. At still higher load conditions (i.e. mid-load conditions), the opening and closing of the valves is timed for tumble flow generation. At full load conditions, both valves are opened and closed at conventional timings to provide the requisite high flow rate and therefore maximize output power.
The present invention has the flexibility to achieve the proper timing of the opening and closing of the intake valves to secure optimum combustion of the fuel under all operating conditions. The opening and closing of the intake valves is varied by the engine controller and is dependent on the engine speed and engine load.